The invention relates to osteosynthetic instruments in general, and more particularly to improvements in so-called external fixation units which can be used to rigidly secure parts or fragments of a broken, cracked or diseased bone to each other for extended periods of time. Still more particularly, the invention relates to novel and improved means for enhancing the versatility and utility of external fixation units.
An external fixation unit which can be used to rigidly connect parts of broken bones is disclosed, for example, in U.S. Pat. No. 4,312,336 to Danieletto et al. The patented fixation unit comprises two spaced-apart clamping devices (hereinafter called holders) for pins which are to be driven into parts of a broken bone at opposite sides of the fracture, and a so-called central body member with a cylinder secured to one of the holders and a rod which is reciprocable in the cylinder and carries the other holder. The cylinder and rod can be fixed to each other to maintain the two holders at a desired distance from one another. In addition, the holders are articulately connected to the respective parts (cylinder and rod) of the central body member by universal joints which can be locked in selected positions. The parts of the patented fixation unit are made of a metallic material. Such so-called unilateral fixation units can be used with advantage to prevent movements of parts of a fractured bone (e.g., parts of tibia) relative to each other.
When a conventional fixation unit is applied to a tibia and the patient is resting on her or his back, the toes of the foot forming part of the injured leg extend upwardly. This renders it necessary to repeatedly or continuously exercise or massage the foot. Fixing of the foot in a desirable normal position by resorting to a rigid bandage is not always possible because such bandage would interfere with blood circulation. Moreover, the foot is likely to have been injured which is another reason why the physician or the nurse cannot resort to a bandage. Exercising or massaging of the foot is not possible if the patient has suffered brain damage, e.g., in the course of an accident which resulted in a fracture of the tibia.
Page 311 of the German-language publication "Manual der Osteosynthese" by M. E. Mueller et al. (Springer-Verlag Berlin Heidelberg New York 1977) shows that an external fixation unit for a fractured tibia can be equipped with a platform which is movable longitudinally of the tibia into or from abutment with the sole of the foot forming part of an injured leg. The fixation unit is a substantially triangular frame having three longitudinally extending frame members, namely two beneath the one at a level above the fractured tibia. The platform for the sole of the foot is movable longitudinally of the two lower frame members toward and away from as well as upwardly and downwardly and laterally of the frame members. Such movability of the platform does not suffice to ensure an optimum orientation of the platform relative to the foot and/or to ensure adequate support for the foot and the ankle of the injured leg.